Consecutive ratio recorder



1951 G. L. BROOMELL, JR

CONSECUTIVE RATIO RECORDER 4 Shets-Sheet 1 Filed June 18, 194.9

. I N VEN TOR. GEORGE L. BROOMELL,JR.

ATTORNEYS Dec. 11, 1951 BRQQMELL, JR 2,577,735

CONSECUTIVE RATIO RECORDER Filed June 18, 1949 4 Sheets-Sheet 2INVENTOR.

GEORGE L. BROOMELLHJR BY ATTORNEYS 1951 G. L. BROOMELL, JR

CONSECUTIVE RATIO RECORDER s Sheets-Sheet 3 Filed June 18, 1949 IN V ENTOR. O R G E L 7 BYOOMELLQR 3 1951 G. 1.. BROOMELL, JR 2 572735CONSECUTIVE RATIO RECORDER Filed June 18, 1949 4 Sheets-Sheet 4 (gINVENTOR. 24 LBRGUMELLIPEFJ Patented Dec. 11, 1951 2,577,735 CONSECUTIVERATIO RECORDER George L; Broomell, J12,

ship,

Lower Gwynedd Town- Montgomery County, Pa.,

assignor to Leeds and Northrup Company, Philadelphia, Pa., a corporationof Pennsylvania Application June 18, 1949, Serial No. 99,997

14 Claims.

This invention relates generally to measuring, indicating, recording, orcontrolling electrical, physical, chemical, or other conditions; and itrelates more particularly to spectroscopic measuring, indicating,recording, or controlling. It is peculiarly applicable where a pluralityof continuously changing conditions are to be treated in sequence. Theword measuring will be used generically hereinafter to includeindicating, recording, or controlling.

Where an accurate comparison of two quantities is wanted ordinary errorsin measuremem of either may result in a relatively great compare tiveerror. However, if the two quantities are so related that both aresubject to like errors the comparison will be accurate. Thisprinciplehas heretofore been recognized, but it has been diffic'ult ofapplication particularly where simultaneous measurement has beenattempted. Simultaneous measurement of the two conditions requiresduplicate apparatus which is unduly expensive and the apparatus may notfunction satisfactorily since differences between the two systems mayresult in a faulty comparison. In accordance with the invention twoelectrical, physical, chemical, or other conditions are mea tired andcompared by successive operation of the same apparatus thereby effectinga true cornparison. These two operations are performed in rapidsuccession in order that time-dependent errors may be minimized.

Particularly where a flowing stream of material is being examined and itis desired to measure an unknown condition in relation to anotherreference condition, it is important that a free choice of the referencecondition be possible; if only a particular reference condition isavailable it may not be subject to the same errors as the conditionbeing measured. The inadequacy of a comparative measurement system inwhich no choice of reference conditions is available will be made clearby reference to Wunsch Patent No. 1,995,594 wherein data is transmittedfrom a remote slidewire to a local slidewire. Provision is made forequalizing the voltages across the two siidewires, but no choice of areference condition other than the full slidewire voltage is possible.Suppose now a portion of the remote slidewire should becomeshortcircuited. The consequent error would not be apparent at the localslidewire and it could not be corrected. Accordingly, it is an object ofthe present invention to measure and compare two conditions, one ofwhich may be chosen arbitrarily anywhere within the scope or field ofmeasurement of the apparatus.

Apparatus of the type herein discussed should ordinarily be capable ofadjustment for operation in a wide field of measurement. For somepurposes it should also be capable of adjustment for automaticallymeasuring in sequence a plurality of conditions. In accordance with theinvention such measurements are made in pairs, each unknown conditionbeing compared to its own reference condition. Thus, a further object ofthe invention is to select successively certain pairs of conditions andto correlate the measurement of these conditions with their selection.

Particularly in making certain mechanical adjustments in the comparisonof the aforesaid two quantities, and in cases where such adjustmentsmust be made rapidly, sustained oscillation or hunting of the system mayoccur. A further object of the invention is to prevent such hunting bymeans which do not detract from the effectiveness of the system. Thisobject is accomplished by suitably regulating the voltage which controlsthe adjustments.

The invention is particularly useful where the conditions to be measuredinclude spectral lines a of radiant energy from a spectrometer and wherethe degree of transmittance of these lines by a material is used toidentify the constituents of the material and to measure the proportionsof various constituents. These measurements may be used merely as asource of information or they may serve as a basis for controlling theproportions of the constituents.

Many substances have the characteristic of absorbing strongly radiantenergy Within a narrow band of wavelengths. Usually the absorption bandfor a particular substance differs sufficiently in wavelength from thebands of other substances so that the mere presence of the absorptionband serves to identify the substance. Thus if the transmittance of asample of an unknown substance is measured at various wavelengths and itis found to transmit well some wavelengths but to absorb, and thereforetransmit poorly, a wavelength of 6.76 microns, it will be known withreasonable certainty that the substance is benzene.

It will be appreciated that this method of analysis is not easy when itis noted that a change from 6.76 microns to about 6.8 microns in thewavelength of the absorption band would have changed the indication frombenzene to isohexadecane, in which case minor absorption bands wouldappear also at about 7.3 microns and 8.05 o

Avery common problem in spectroscopic analy- 3 sis, and the one whichwill be described herein as an example, is where it is known thatcertain constituents are present, in a continuously flowing sample ofmaterial and it is desired to determine and record the relativeproportions of the constituents. In addition to the above-mentionedproblem of determining the wavelength of certain absorption bands withgreat precision, there is considerable difiiculty in detecting andmeasuring the magnitude of the energy in the absorption band passingthrough the sample. Most of the energy from the source has beendiscarded as a result of the selection of the narrow band of wavelengthsthat are used so that only a small amount of energy passes through thesample to the detector. A common detecting device is a thermocouple inwhich temperature differences amounting to only a few millionths of adegree centigrade must be measured to achieve an accuracy of energymeasurement of per cent. It is apparent that absolutemeasurement of thetransmittance of a sample would require great care to eliminate spurioustemperature effects and numerous other sources of error. On the otherhand, the relative transmittance of the sample at two similarwavelengths may be measured despite these errors, and such relative measurements are highly useful provided the reference wavelength is properlychosen. A further object of the invention is to measure thetransmittance of a sample at a predetermined wavelength relative to thetransmittance at any desired reference wavelength, and automatically torepeat this measurement so that any remaining errors may be reducedfurther, if desired, by averaging a large number of readings. Anotherobject is to so measure the transmittance of a sample at a number ofwavelengths, each with respect to its own reference wavelength, and torepeat the sequence of measurements automatically.

Other objects and advantages of the invention will be apparent from thefollowing more detailed description thereof with reference to theaccompanying drawings, in which:

Fig. l is a diagrammatic representation of a spectroscopic analyzerembodying the invention;

Figs. 2, 3, 4, 5, 6, and '7 are simplified fragmentary schematic viewsof a portion of the analyzer shown in Fig. 1, each illustrating theoperative connections of certain parts for differing positions of theswitching arrangement;

Fig. 8 is a fragmentary diagrammatic view of a hypothetical recorderchart used to explain the operation of the invention;

Fig. 9 is an enlarged fragmentary perspective view of a portion of theapparatus shown in Fig. 1; and

Fig. 10 is a fragmentary diagrammatic view of a modification of thestructure shown in Fig. 1.

Referring to Fig. 1, radiant energy from source H] is directed tothermocouple l I by mirrors l2a, [2b, [20, l2d, 12c, 12 and l2g throughsample cell I3, slit l6, and prism 55. As is well known, the radiantenergy is dispersed by prism l5 and only the energy within a certainnarrow band of wavelengths is focused on thermocouple H by concavemirror 12g. Thus, the system including prism l5 and mirror 12g serves toselect and apply to thermocouple H a particular wavelength and thiswavelength may be varied by varying the angular position of prism l5.

Thermocouple ll produces a voltage depending upon the temperaturedifference of its elements which, if there are no spurious temperatureeffects or other errors, is proportional to the transmittance ofwhatever material is in sample cell [3. Soure I!) may, if desired, be asuitably heated silicon carbide rod in which case prism ['5 and thetransparent ends of sample cell [3 may be made of some salt such aslithium fluoride.

To eliminate or minimize certain errors due to space variation ofambient temperature at thermocouple ll, shutter I6 rotating at about '7revolutions per second by motor 16a interrupts the flow of radiantenergy in synchronism with the interruption of an electrical current bycommutator H. In order that the voltage from thermocouple II, which maybe of the order of one millionth of a bolt, may be amplified byalternating-current amplifier l9, it is reversed about 150 times persecond, to give a '75-cycle voltage, by commutator l8. Commutator 20operating in synchronism with commutator [8 from motor 16a rectifies the-cycle output from amplifier [9. There remains in the rectified outputthe 7-cycle variation introduced by the shutter Hi. The rectifying ordetecting action of commutator I1 is balanced by slidewire 2|.Commutator I1 is synchronously driven with shutter 16 to rectify the7-cycle output. Any remaining alternating component of voltage isremoved by filter 22 so that a substantially pure D. C. voltage isapplied from the above-described detector system to slidewire 23 throughone of the bank of rheostats 24 and section 25a of selector switch 25.Thus, there is applied across the end terminals of slidewire 23, andtherefore to contact 26, a signal voltage which depends upon thematerial in sample cell 13, the rotary position of prism l5, and theresistance of the particular rheostat to which contact is made byselector switch 25. If the rheostat and prism positions are fixed, thenthe signal voltage at contact 26 is a measure of the transmittance ofthe material within sample cell [3, subject to necessary errors.

Suppose, by means described hereinafter, prism I5 is positioned toprovide at thermocouple II the wavelength which it is desired to utilizefor reference purposes for subsequent measurement at a differentwavelength. It is then desired to position contact 26 of slidewire 23inversely in proportion to the voltage across slidewire 23, that is tosay, it is desired to set contact 26 higher if the reference voltageapplied to the whole of slidewire 23 be low, or to set it lower if thereference voltage be high. When a voltage to be measured is appliedsubsequently to slidewire 23, it will result in a voltage at contact 26which is in a certain ratio to the total voltage and that ratio will bedetermined by the position of contact 26. In other words, a fraction ofthe voltage to be measured is applied to the measuring circuit, and thatfraction is inversely proportional to a reference voltage.

To show an advantage of this arrangement, suppose it is used to measurethe transmittance of a material at a certain wavelength, and thatthereafter some dust on prism E5 or the various mirrors reduces theradiant energy at thermocouple H sufficiently to reduce the voltage atslidewire 23 by 10 per cent. This would mean a 10 per cent error ifabsolute measurements were relied upon. In accordance with the inventionit would mean merely that contact 26 would be set a little higher onslidewire 23, since the dust on prism 15 would reduce the referencevoltage by the same percentage that it reduced the measuring voltage, sothat a larger fraction of the total slidewire voltage would appear atcontact 26. By reason of the foregoing corrective action,

the voltage measured at contact 26 thus would be unchanged and the dustwould cause no error.

' This positioning of contact is accomplished by providing a servosystem to move it to a fixed voltage point or, mor specifically, contact26 is moved by the servo system until the difference between its voltageand the voltage of point 2'! associated with slidewire 35 issubstantially zero. If a reference wavelength that produces a strongreference voltage is chosen, contact 26 will be moved to a point nearground potential, whereas if a weak reference voltage is used, contact26 will be moved to a point far from ground potential.

An advantage of the invention is the independent adjustability of theattenuation channels provided by rheostats 24. In general, thetransmittance of the material in sample cell 13 will vary widely atdifferent wavelengths so that, without adjustment, the trace at somepoints, Fig. 8, might be deflected too much or too little. By adjustingrheostats 2:? after determining the transmittance characteristics of thesample at various wavelengths, the most useful portion of the trace maybe kept at substantially full scale at all of the wavelengths at whichtransmittance measurements are made.

Now suppose that, by means hereinafter described, prism I5 is rotated toa position which will result in a wavelength at thermocouple II at whichit is desired to measure the transmittance of the material in samplecell 13. This rotation of prism !5 will be accompanied by movement ofcontact 28a of selector switch 25 from the first attenuation channel,rheostat 24a,

sponding in voltage to that of contact 26, and

pointer 3i operatively connected to contact 29 now indicates on scale 32the transmittance of the material in sample cell [3 at the predeterminedwavelength in terms of the position of contact 25. In other words, theposition of contact 2% determines the fraction of the total slidewirevoltage to which contact 29 is adjusted.

Slidewire 3d, and consequently point 21, is supplied with substantiallyconstant voltage from battery 33 adjustable by rheostat 34. However, thevoltage from battery 33 is not critical and it may vary over aconsiderable range provided its variation is slow enough so that thechange between calibrations is negligible.

From the foregoing description it will nowbe apparent that there isfirst established a balanceable network (Fig. 2) in which the referencesignal voltage from filter 22 produced by the detector-amplifierarrangement is balanced by the adjustment of contact 26 of slidewire 23,the balanceable network being supplied with a fixed voltage from battery33. After balance of this network and a predetermined time interval thecircuit connections are changed by timing switch means to establish asecond balanceable network, also supplied by the battery 33, to whichthere is applied through the same filter 22 the voltage to be measured.In this case the contact 26 of slidewire 23 remains stationary, itsadjustment having been completed for establishment in the secondbalanceable network of a reference condiwire at and at the same timedrives the pen or indicator relative to the associated scale or chart toprovide a record and indication of the magnitude of the unknown voltageunder measurement.

The servo system which adjusts contact 26 comprises motor 35, amplifier35 and accessory apparatus. Motor 35 may be a two-phase induction motor,one of its phases being supplied by any suitable alternating-currentsupply lines 37, and phase 38 being supplied by amplifier 3B. The D.-C.voltage between contact 26 and point 2'. is converted to alternatingcurrent in vibrator 3% for amplification in transformer 40 and amplifier35 as described in the prior patent to Williams, No. 2,113,164.Resistors ll and capacitors 42 to stabilize the sevro system by what iscommonly known as derivative control, and resistors 43a, 43b, 43c and43d tend further to stabilize the servo system by equalizing itssensitivity throughout the range of slidewire 23.

The voltage between contact 25 and point 21, through a switching systemto be described hereinafter, a constitutes a servo error voltage whichthe servo system reduces to zero by movement of contact 26. From theservo system standpoint slidewire 23 may be regarded as a voltagepickoif device and any other suitable well-known pickoif device may beemployed.

When contact 29 is to be adjusted, main servomotor =24 is substitutedfor calibrating servomotor 35 by switch 45. Motor 44 also drives pointer3i and pen as which records on record chart t? the posititon of contact29. Slidewire 30 may appropriately be called a main or recordingslidewire, while slidewire 23 may be called a calibrating slidewire.Record chart 4'1 is moved continuously by timing motor 48 which may be asingle-phase synchronous motor operated from power line 3?. Motor 48also drives continuously a cam system, including shifter cam 49, motorselector cam 59, and cycle-control selector cam 5!, or equivalent meansfor operating timing switch means or devices. Cam 5d throws motorselector switch to connect amplifier 3% to either motor 35 or motor 44.

Cam 49 lifts follower 52 to move shifter switch contact 53 from point Lto point K, thereby shifting the part of the circuit to which contact 26is connected from point 21 to contact 29 of slidewire 30 if contact 221)of selector switch 25 is connected to'conductor 9, in which positions ofcontact 28b prism 15 is positioned by means hereinafter described toproduce at thermocouple I i one of those wavelengths which it is desiredto use as reference wavelengths. If contact 28b is in one of thealternate positions, connected to contact 29, in which position prism IEwill be positioned to produce at thermocouple I! one of the wavelengthsat which the transmittance of the material in sample cell I3 is to bemeasured, movement of follower 52 to move shifter switch contact 53 willhave no effect.

After contact 26 has been adjusted to make its voltage equal to that ofpoint 21, the position of contact 26 being determined by thetransmittance of the material in sample cell H3 at a referencewavelength, and cam 56 has thrown motor selector switch 45 to transferamplifier 36 from motor 35 to 4'4, cam 43 transfers the servo input frompoint 21 to contact 29 whereupon contact 29 is moved by the servo systemuntil its voltage is equal to that of contact 26. Inasmuch as thevoltage at contact 28 previously was adjusted to equal that at point 27,and since this adjustment has not been disturbed, contact 29 is moved toa point whose voltage is equal to that of point 21. This will placepointer 3| at what may be regarded as its full-scale position. Next, cam5| closes cycle-control selector switch 54 to cause selector switch tomove to a new position in which a wavelength is produced at which itisdesired to measure the transmittance of the contents of sample cell l3,this new wavelength resulting in a different voltage at contact 26, thusunbalancing the system and causing contact 29 to be readjusted tomeasure and record the transmittance.

Having thus measured and recorded the transmittance of the material insample cell [3 at one predetermined wavelength, after a predeterminedtime interval, cam 5| then closes momentarily switch54 causing selectorswitch 25 to move to another position in which contact 280. is connectedto rheostat 240. This movement of selector switch 25 produces threeresults.

First, by manual adjustment of rheostats 24 the independent adjustmentof the attenuation of the voltage originating in thermocouple H ispossible to compensate for strong or weak transmittance of the materialin sample cell I3 at the particular wavelength applied thereto. Inaddition to advantages already described, substantlally the full rangeof slidewire 23 may thus be utilized. If, with a strong referencesignal, contact 26 were adjusted near the low-voltage end of slidewire23, inaccuracies might occur, since slidewire 23 may be of a woundconstruction that may be adjusted only in discrete steps, and one ofthese steps might be a large part of the remaining resistance thusprecluding a fine adjustment. It will be understood that either thecontacts or the bodies of the slidewire described herein may be movable.

Second, in section 25b of selector switch 25 contact 2812 is moved to aposition which permits cam '49 to transfer the servo input circuit fromcontact 29 to point 2'! in readiness for the readjustment of contact 25by motor which has been connected to amplifier 36 by cam and switch 45.

Third, contact 280 of section 250 of selector switch 25 moves to openthe circuit which includes contact of positioning switch 56 and limitswitch 51, thereby allowing relay 58 to resume'its normally closedposition to connect motor 59 to power lines 31, thereby to rotate prisml5 to a predetermined position which will result in the next desiredreference wavelength at thermocouple The rotation of prism motor 59 alsoultimately moves contact 55 of sequence switch 56 to a position oppositecontact 28c, and it closes limit switch 51, thereby completing the powercircuit to relay 58 to open the relay and stop motor 59. In themeantime, prism l5, Figs. 1 and Q, has been positioned as follows: cam60 is driven by motor 59 to actuate limit switch 51 operativelyconnected to bell-crank 5| or an equivalent mechanical or electricallinkage. Connecting rod 62 eccentrically connected to cam 60 by pin 63lifts lever 64 from stop 65 and maintains it in a lifted positionthroughout a portion of a revolution of cam Gil. While lever 64 is solifted, motor 59 rotates turret 55 until another stop 61 is under lever64, whereupon spring 68 holds lever 54 against stop 61 during the otherportion of a revolution of cam 65. Cam 60 is rotated one revolutionwhile turret 55 moves the distance between two stops by any suitablewell-known gearing, such as worm 59a meshing with gear 5%.

Pin 63 is sufiiciently eccentric on cam 60 to lift lever 64 more thanenough to clear the longest stop on turret 66, the excess movement ofconnecting rod 62 being accommodated by its free movement along lever 64between pins 69 and 10. Each of the stops on turret 66 is threadedtherein for adjustably positioning lever 64 and prism I5, attachedthereto, so that adjustment of any stop assures that, during the time itpositions lever 64, prism l5 will be positioned to produce atthermocouple ll an accurately predetermined wavelength.

It will now be apparent that movement of contact 280 of selector switch25 to a new position will result in the selection of a new wavelength byprecisely positioning prism I5 carried by lever 54, the lever being heldfirmly against a precisely adjusted stop, while the prism drive motor 59is stopped at only a roughly predetermined position by closing of limitswitch 51 and the movement to a new position of contact 55 ofpositioning switch 55, the new position of contact 55 corresponding tothe new position of contact 280 thereby assuring that the correct one ofseveral predetermined wavelengths is produced.

Switches 25 and 55 may be of any suitable well-known type, and they maybe circular in configuration with each switch position corresponding toa stop on turret 55. Switch 25 may be operated directly from timingmotor 44' and cam 5|, if desired, instead of switch 54 and battery 54a.

In the preferred form of the invention, the recording mechanism ispreferably of the multiplepoint printwheel type, such as shown in Rossand Seberhagen Patent No. 2,113,748. The first recorded point will bethe one indicating that the system has been calibrated in accordancewith a reference voltage representative of the transmittance at aselected reference wavelength, and the next recorded point will beindicative of the value of the unknown voltage representative of thetransmittance at a selected measuring wavelength in relation to thisreference voltage; i. e., the ratio of one to the other. However, for amore detailed explanation of the present invention, an

idealized trace has been shown in Fig. 8, such as might be made with thepen 46 continuously in engagement with the record chart 4? and withstraighteline movement of the pen. Hence, the idealized trace 0r" Fig. 8can be utilized in the present description both as a timing diagram andas a measurement record of one transmittance with reference to theother.

In Figs. 2-7 the circuit of Fig. 1 has been shown with certain switchesomitted for clearness, each figure representing a different switchingposition. The circuit connections of Fig. 2, wherein contact 26 ispositioned inaccordance with the transmittance of the material in samplecell l3 at a reference wavelength, are maintained during the timeinterval between points A and B of Fig. 8. With contact 53, Fig. 1, incontact with point L and selector switch 25 positioned to receive asignal through rheostat 24a, it will be apparent that contact 29 is notconnected to any other circuit element and that the servo error voltageis the voltage between contact 26 and point 21. Cams 49, 5D, and 5| arein the positions shown in Fig. 1.

At point B the circuit connections change to those shown in Fig.3wherein cam 50 has been operate in this condition since no change hasbeen made in the servo error voltage. which rey mains at zero. Pen 66will remain in its previous position as indicated by the trace betweenpoints A and B in Fig. 8, thus extending the tracefrom point B to pointC.

At point C the circuit connections change to those of Fig. 4 wherein cam48 has operated to throw contact 53 from point L to point therebyshifting the servo input circuit from point 2'! to contact 29. Motor Mimoves contact 2a to a point whose voltage is equal to that of contact25, and pen 46 moves with contact 29 to point D, 3, where it remainsduring the time interval between D and E. Since contact 25 remains atthe same voltage as point 2?, contact will now be set at a point whosevoltage is the same as t: point 27. The voltage point 2' is so less thanthe full voltage of slidewire 3S1, determined by resistor l l, in orderthatcontact may move to a slightly higher voltage position, as may do ifthe setting of contact 23 is in error. Since rheostats 2 ordinarily areso adjuster. that the voltage applied to slidewire 23 with measuringwavelengths will not exceed the voltage with reference wavelengths,contact 29 usually will be at a voltage less than that of point 2? and,therefore, resistor ii is so chosen that pen 4% is nearer one edge ofthe record chart 4?, making trace like that shown between points D and Ein Fig. 8 with the circuit arrangement shown in 4. The straight linebetween D and E shows that the adjustment of contact 25 relative toslidewire 23 has been completed and visually indicates the measuringsystem is in readiness to measure the transmittance at themeasuringwavelength.

At point E the circuit connections change to those of Fig. 5, whereincam 55 and switch have actuated selector switch 25 to move i s contact28 to rheostat 24b and to rotate prism l5 to a position determined byanother stop, thereby producing at thermocouple l a wavelength at whichit is desiredto measure the transmittance of the material in sample celll3. Inasmuch as this transmittance will differ from that at thepreviously used wavelengths, and since rheostat 2 32) may have adifferent resistance from rheostat 240., the voltage applied. toslidewire 23, and therefore the voltage at contact will now be differentfrom the voltage at contact thus unbalancing the system and providing aservo error voltagethat ill cause motor 44 to rotate contact 29 torebalance it by making the voltage at ccntact 29 equal to the voltage atcontact i=5. Pen 4'3 is thereby driven to point F on the chart to recordthe measurement of the transmittance at the measuring wavelength interms of the transmittance at the reference wavelength. shown in Fig. 8,the pen remains for an -Jterval of time in its last-named position.Thus, it will be seen adequate time is provided for a balancing andprinting operation during the time between points D and E and betweenthe points F and G.

- Such printed points i and 2 have been shown within the small circles.At point the circuit connections at the latter point change from thoseof Fig. 5 to those of Fig. '3.

In 6, cam 5i and switch as have caused selector switch 25 to move itscontact 28 to make contact with rhecstat 24c and to set prism 5 toproduce a new reference wavelength at thermocouple 5 5. Due to thedifferent transmittance of the material in sample cell H3 at the newreference wavelength, and because of the diiferent resistance ofrheostat 240, the voltage at contact 26 will be different, therebyunbalancing the servo system and causing contact 23 to move to a newposi ions cbast tr c rded b een int and A of Fig. 8-. As a matter oftransition, when the circuit connections chang from ig. 5 to those ofFig. 6, it will be observed that he transmittance at the new referencewavelength will be measured in terms of the preceding referencequantity, this operation appearing on the trace between the points H andA, as mentioned.

At the point A. the connections chan e to those of Fig. '7 and a newcycle is initiated. in Fig. '7 cam 49 has operated to shift the servoinput circuit from contact 29 to point 21, this being the same circuitarrangement shown in Fig. except that the first of a diiferent pair ofattenuation channels E ic, utilize instead of 24a and a differentreference wavelength has been produced. The other channel of this pairis provided by rheostat Zed. In this circuit arrangement contact will bereadjusted, and pen remains stationary since motor 44 is nowinoperative, cam and switch 45 I)?" he connected motor 35 to amplifier35.

Reference is made to the fact that with the multiple-point recorder,printing does not occur except at a point during the intervals between Dand E and a point between F and and that for successive measurements ofa plurality of quantities, each in relation to its own referencequantity, the reference points may be designated as odd numbers such asl. and the measured points designated by even numbers such as 2.

Ehere has been described a system wherein a slidewire is frequentlyadjusted to make the voltage of its contact 25 equal to a fixed voltage,that of point 2i, by a servo system. It is well known that servo systemsthat respond quickly and accurately to unbalance, or error, voltagestend to be unstable and numerous antihunt de vices have been proposedfor their stabilization. None of these devices by themselves have beensatisfactory in the measuring system of the invention because of thefollowing circumstance. ihe voltage applied to slide-wire 23 is subjectto wide variation depending upon the transmittance of the material insample cell It and the adjustment of rheostats 24. Accordingly, thecurrent through slidewire 2S varies widely and. therefore, if theslides/ire be linear, there will be wide variation in the effect on theerror voltage of a small movement of contact such as will. occur as theservo system approaches a balanced condition.

If the voltage applied to slidewire be high so that contact 26 balancesnear the lower end of the slidewire, a given movement of contact willcause a chan e in its voltage that is relatively great because of therelatively great current in the slidewire. On the other hand, if thevoltage applied to slidewire 23 be low, its current will be low and thesame movement of contact 25, balancing high up on the slidewire, willcause relatively little effect on the error voltage.

Antihunt devices heretofore known, such as the derivative controlcircuits including resistors 5i and capacitors :32. will be fullyeffective only if the piokoif sensitivity is substantially constant overthe range of operation of the pickoff device; that is to say, a givenmovement of contact 25, or other pickoif element, must producesubstantially the same change in its voltage whether the current throughthe slidewire be high so that the contact is low down on the slidewirewhen its voltage equals the fixed voltage. or whether the slidewirecurrent be low 11 so that the contact balances high up on the slidewire.It is deemed preferable to make a relatively simple provision in thesystem that will render existing, well-known antihunt devices effectivetherein, rather than to provide a wholly new antihunt device.

Stated mathematically the requirement is that By the nature of theproblem, the current 2' through the slidewire is constant during thetime the contact is being adjusted so that ezir (C) and where 1' is theresistance of the slidewire up to the contact. Substituting Equation Din Equation C Substituting Equation E. in Equation B, the requirementbecomes This requirement will be met if the slidewire is so designedthat log 1- K That this is so can be shown by differentiating Equation Gwith respect to 1'.

which is identical to Equation F. A slidewire designed so that theposition of its contact is proportional to the logarithm of theresistance of the slidewire up to the contact, in accordance withEquation G, is referred to herein for convenience as a logarithmicallytapered slidewire.

There has been described an analyzer system with a switch 45 forconnecting either of two motors 35 or 44 to amplifier 36 to perform twodifferent functions. In Fig. a modification of this arrangement is shownin which a single servomotor E2 permanently connected to amplifier 36 iscaused to perform similar functions when cam 50 moves rotor 13 againstthe tension of spring '14 to rotate by frictional contact disc 15 whichis connected to contact 25. In this po sition' servomotor 72 movescontact 26 in the same way that servomotor 35 moves contact 26 in themodification shown in Fig. 1. In the other position of cam 511 spring Mholds rotor 13 against disc '55 to drive contact 29, pointer 3!, and pen48. In this position servomotor i2 adjusts contact 29 in the same waythat servomotor 44 adjusts contact 29 in the arrangement shown in Fig.1.

While preferred embodiments of the invention have been shown, it will beunderstood that modifications thereof may be made within the spirit andscope of the invention as set forth in the appended claims.

What is claimed is:

1. A measuring system comprising a balanceable network including acalibration slidewire and a main slidewire, circuit-controlling meansfor applying to said network a signal varying in accordance with themagnitude of an arbitrarily selected reference condition for unbalancingsaid network, means responsive to the unbalance of said network foradjusting said calibration slidewire in a direction and to an extentsufficient to rebalance the network, said unbalance-responsive meansbeing connected between the movable contact of said calibrationslidewire and a fixed voltage point, said circuit-controlling meansbeing operable after the rebalancing of said network to apply to saidnetwork a signal varying with the magnitude of a different condition andto connect said unbalance-responsive means between said movable contactof said calibration slidewire and the movable contact of said mainslidewire for adjustment of said main slidewire in the direction and toan extent sufficient to equalize the voltages at said movable contactsof said slidewires to rebalance said network thereby to provide ameasurement of the magnitude of said second-named condition with respectto the magnitude of said first-named condition.

2. The combination set forth in claim 1 in which saidcircuit-controlling means is operable from one position to another aftera predetermined time interval in each position thereof, and means underthe control of said circuit-controlling means for controlling theapplication of said signals from said two conditions to said network intimed relation with the operation thereof.

3. The combination set forth in claim 1 in which the conditions undermeasurement are spectral lines of a spectrometer and in which there isprovided means operable in timed relation with said circuit-controllingmeans for scanning predetermined spectral lines as standards and foralternately scanning lines for determination of the intensity of eachwith respect to one of said spectral lines selected as standards.

4. In apparatus for measuring the transmittance of a sample at apredetermined wavelength in relation to the transmittance of said sampleat an arbitrarily selected reference wavelength, the combination whichcomprises a spectroscopic analyzer for producing a voltage substantiallyproportional to the transmittance of said sample at any operatingwavelength of said analyzer, said analyzer being operable at variouspredetermined wavelengths, a balanceable network including a calibrationslidewire, a main slidewire, a selector switch and servo system foradjusting said calibration slidewire relative to its contact inaccordance with the difference between a fixed voltage and said analyzervoltage at a reference wavelength and without further adjustment of saidcalibration slidewire thereafter adjusting said main slidewire relativeto its contact in accordance with the unbalance of said networkresulting from application thereto of said analyzer voltagecorresponding with said predetermined wavelength to equalize thevoltages at said slidewire contacts, and timing switch means operativelyconnected to said servo system, selector switch, and analyzer forcontrolling the sequential selection and utilization ofcertainpredetermined wavelengths.

5. In apparatus for measuring and comparing predetermined quantities inrelation to arbitrarily selected reference quantities having similarcharacteristics and being subject to similar measuring errors, thecombination of a detector system for producing a voltage substantiallyproportional to any one of various predetermined quantities, and ameasuring systemcomprising a balanceable network including a calibrationslidewire, a main slidewire, a selector switch and servo system foradjusting the contact voltage of said calibration slidewire inaccordance with the relation between a fixed voltage and said contactvoltage for a selectedcne of said reference quantitles and thereafteradjusting said main slidewireto balance its contact voltage andthevoltage at the contact of said calibration slidewire fora selected oneof said predetermined quantities, and timing switch means operativelyconnected to said servo system, selector switch, and measuring systemthereby to control the sequential selection and utilization of certainof said predetermined quantities.

6. A measuring system comprising abalanceable network including acalibration slidewire, a main slidewire, an indicator operativelyconnected to said main slidewire, a selector switch for, applying tosaid network a signal varying in accordance with the magnitude of anarbitrarily selected reference condition for unbalancing said network, aservo system responsive to the unbalance of said network for adjustingsaid calibration slidewire in a direction and to an extent sufiicient torebalance said, network, said servo system being connected between themovable contact of said calibration slidewire and a point of saidnetwork correspondin in voltage to a fixed point on said main slidewire,said selectorswitch being operable after rebalance of said network toapply to said network a signal varying with the magnitude of a differentcondition, and timing switch means to connect said servo system betweensaid calibration slidewire and said main slidewire for adjustment ofsaid main slidewire in a directionand to an extent sufiicient toequalize the contact voltages of said slidewire to rebalance saidnetwork thereby to provide a measurement of the magnitude of saidsecondenamed. condition with respect to the magnitude of saidfirst-named condition in avoidance of measuring errors common to. bothconditions.

7. The combination set forth in claim 6 in which said selector switch isoperable automatically from one position to another after apredetermined time interval in each position thereof, a section of saidselector switch being adapted and arranged for controlling theapplication of said signals froinsaid two conditions to said network intimed relation with the operation thereof.

8. The combination set forth in claim 6 in which the conditions undermeasurement are spectral lines of a spectrometer and in which there isprovided spectrum scanning means operable in timed relation with saidselector switch for scanning predetermined spectral lines as standardsand for subsequently and alternatelyscanning spectral-lines fordetermination of the intensity of each with respect to one of saidspectral lines selected as standards.

its members the portion of said said voltage output to said network foradjusting 9. The combination set forth in claim 6-111 which theconditions under measurementare spectral lines of a spectrometer and inwhich there is provided spectrum scanning means operable in timedrelation with said selector switch for scanning predetermined spectrallines as standards and for alternately scanning lines for determinationof the intensity of each with respect to one of said spectral linesselected as standards.

10. In a spectroscopic analyzer having a sample cell adapted andarranged to expose the contents thereof to radiant energy from a sourcehaving a spectrum of substantial width, a spec-. troscope for selectingby the position of one of its members the portion of said spectrum towhich said contents are exposed, and a detector amplifier having avoltage output substantially proportional to the transmittance of saidcontents at the portion of said spectrum selected by said spectroscope,the combination therewith of a balanceable network including acalibration slidewire, a main slidewire, and an indicator operativelyconnected to said main slidewire, aselector switch for applying to saidnetwork said voltage output to unbalance said network, a servo systemresponsive to the unbalance of said network for adjusting saidcalibration slidewire in a direction and to an extent sufficient torebalance said network, said servo system initially being connected toand controlled by the volte age between the movable contact of saidcalibration slidewire and a fixed point on said main siiclewire, saidselector switch being operable after rcbalance of said network to applyto said network the voltage output of said amplifier at differentportion of said spectrum, and timing switch meansto connect said servosystem between the movable contacts of said calibration slidewire andsaid main slidewire for adjustment of said main slidewire in thedirection and to an extent sufficient to rebalance said network therebyto measure the transmittance of said contents at said second-namedportion of said spectrum in relation to the transmittance of saidcontents at said first-named portion of said spectrum. in avoidance ofmeasuring errors common to measurement of the transmittance at both saidportions of said spectrum.

11. In a spectroscopic analyzer having a sample cell adapted andarranged to expose the contents thereof to radiant energy from a sourcehaving a spectrum-of substantial width, a spectroscope for selecting bythe position of one'of spectrum to which said contents are exposed, anda detectora nplifier having a voltage output substantially proportiQnalto the transmittance of said contents at the portion of said spectrumselected by said spectroscope, the combination therewith of abalanceable network including a calibration slidewire, a main slidewire,and an indicaa selector switch for applying to said network unbalancesaid network, servo system responsive to the unbalance of saidcalibration slidewire in a direction and to an extent sufiicient torebalance said network, said servo system initially being connected toand controlled bythe voltage between the movable contact of saidcalibration slidewire and a fixed point onsaid main slidewire, saidselector switch being operable'after-reba-lance of said network to applyto said network the voltage output of said amput through plifier at adifferent portion of said spectrum, and timing switches to connect saidservo system between the movable contacts of said calibration slidewireand said main slidewire for adjustment of said main slidewire in thedirection and to an extent sufficient to rebalance said network, saidspectroscope, selector switch, and timing switches being interconnectedto operate successively in predetermined time relation thereby,

to measure the transmittance of said contents at certain portions ofsaid spectrum in relation to the transmittance of said contents atcertain different portions of said spectrum in avoidance of measuringerrors common to measurement of the transmittance of said contents atall said portions of said spectrum.

12. In a spectroscopic analyzer having a sample cell adapted andarranged to expose any contents thereof to radiant energy from a sourcehaving a spectrum of substantial width, a spectroscope for selecting bythe position of one of its members the portion of said spectrum to whichsaid contents are exposed, a detectoramplifier having a voltage outputsubstantially proportional to the transmittance of said contents at theportion of said spectrum selected by said spectroscope, and a pluralityof pairs of independently adjustable attenuation channels thecombination therewith of a calibrating slidewire having a relativelymovable voltage contact,

a selector switch for connecting said voltage outa selected one of saidchannels across said slidewire, a calibrating servomotor for moving saidslidewire relative to said contact, an indicator, a main slidewirehaving a relatively movable voltage contact, a main servomotor formoving said indicator and said main slidewire relative to saidlast-mentioned contact, a timing motor and a cam system driven thereby,cam, a shifter cam, and a selector cam for actuating said selectorswitch, a tapped resistor and a fixed voltage source each in shuntrelation to said main slidewire, an amplifier having an outputoonnectable by operation of said motor cam to either of saidservomotors, said amplifier having an input connected to said contact ofsaid calibrating slidewire and being oonnectable by operation of saidshifter cam to either said contact of said main slidewire or to a tap ofsaid resistor, said amplifier being adapted and arranged for operationof the servomotor to which it is connected to equalize the voltages atits input, said cam system being adapted and arranged first to causeadjustment of said calibrating slidewire contact voltage from one ofsaid channels to equal the voltage of said tap on said resistor andsubsequently to cause adjustment of said main slidewire contact voltageto' equal the voltage of said calibrating slidewire contact from anotherof said channels, a prism motor for rotatin said spectroscope member, alimit switch for stopping said motor approximately at a predeterimnedposition of said memher, a stop carried by a rotatable turret driven bysaid prism motor for positioning more accurately said member, and asequence switch connected to said turret in series with said limitswitch and operatively connected to said selector switch wherebyselected portions of said spectrum are utilized for measuring inrelation to other predetermined portions thereof.

13, In a measuring system for measuring and comparing a condition inrelation to an arbitrarily said cam system comprising a motor selectedreference condition having similar characteristics and being subject tosimilar measuring errors, the combination of a balanceable networkincluding a calibration slidewire and a main slidewire,circuit-controlling means for applying to said network a signal varyinin accordance with the magnitude of a condition for unbalancing saidnetwork, means responsive to the unbalance of said network for adjustingsaid calibration slidewire in a direction and to an extent sufficient torebalance the network, said unbalance-responsive means being connectedbetween the movable contact of said calibration slidewire and a fixedvoltage point, and means for connecting said unbalance-responsive meansbetween said calibration slidewire and said main slidewire for adjustingsaid main slidewire with respect to said calibration slidewire forequalization of the contact voltages of said slidewires, saidcircuit-controlling means being operable after the rebalancing of saidnetwork to apply to said network a signal varying with the magnitude ofa different condition and to connect said unbalance-responsive meansbetween said movable contact of said calibration slidewire and themovable contact of said main slidewire for adjustment of said mainslidewire in a direction and to an extent suflicient to equalize thevoltages at said movable contacts of said slidewire to rebalance saidnetwork thereby to provide a measurement of the magnitude of saidsecondnamed condition with respect to the magnitude of said first-namedcondition.

14. A measuring system comprising a balanceable network including alogarithmically tapered calibration slidewire and a main slidewire,circuit-controlling means for applying to said network a signal varyingin accordance with the magnitude of an arbitrarily selected referencecondition for unbalancing said network, means responsive to theunbalance of said network for adjusting said calibration slidewire in adirection and to an extent suflicient to rebalance the network, saidunbalance-responsive means being connected between the movable contactof said calibration slidewire and a fixed voltage point, saidcircuit-controlling means being operable after the rebalancing of saidnetwork to apply to said network a signal varying with the magnitude ofa difierent condition and to connect said unbalance-responsive meansbetween said movable contact of said calibration slidewire and themovable contact of said main slidewire for adjustment of said mainslidewire in the direction and to an extent sumcient to equalize thevoltages at said movable contacts of said slidewires to rebalance saidnetwork thereby to provide a measurement of the magnitude of saidsecond-named condition with respect to the magnitude of said first-namedcondition.

GEORGE LL BROOMELL, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Moore Oct. 19, 1948

